1. Field of the Invention
The present invention generally relates to a semiconductor device, and more particularly, to an improved semiconductor device in which a fuse portion is made more resistant to moisture.
2. Description of the Background Art
FIG. 13 is a top view of a conventional semiconductor device which includes a fuse portion. FIG. 14 is a cross sectional view of the fuse portion of the semiconductor device shown in FIG. 13, taken along the line XIV--XIV. With reference to FIGS. 13 and 14, a first circuit 4 and a second circuit 5 are provided on a semiconductor substrate 1, spaced apart from each other. First circuit 4 and second circuit 5 are connected by a fuse portion 2. Fuse portion 2 is protected by an insulating film 3 provided on semiconductor substrate 1.
In the conventional semiconductor device, fuse portion 2 is made of the same material (Al, W or Wsi) as interconnections in circuits 4, 5.
FIG. 15 is a top view of a semiconductor device, illustrating the condition after laser blowing. FIG. 16 is a cross sectional view of the semiconductor device taken along the line XVI--XVI in FIG. 15. Blown by laser, fuse portion 2 is severed, so that first circuit 4 is electrically separated from second circuit 5. In a portion 6 where fuse portion 2 has been cut off, the oxide film 3, which had been covering the top of the fuse portion 2, is broken at the same time. Consequently, the end surface 2a of fuse portion 2 is exposed to moisture entering from the top.
FIG. 17 is a diagram illustrating a problem encountered by the conventional semiconductor device. FIG. 18 is a cross sectional view of the device taken along the line XVIII--XVIII in FIG. 17.
In the conventional semiconductor device, referring to FIGS. 17 and 18, the end surface 2a of the fuse portion is exposed to moisture entering from the top. If fuse portion 2 is made of a material which is vulnerable to moisture, corrosion will advance to fuse portion 2, and will destroy the interconnections in circuit 5 and also other fuse portions, thus resulting in a defective device. In FIGS. 17 and 18, a corroded portion in fuse portion 2 is denoted by a reference numeral 29.
Generally, a fuse portion is made of a conductive layer. However, it is very difficult to select for the fuse portion a material highly resistant against corrosion, because higher priority is given to a material which will guarantee a reduction in layout and easiness of blowing.
FIG. 19 is a top view of a conventional semiconductor device in which a fuse portion is divided and separately arranged in two locations. FIG. 20 is a cross sectional view of the device taken along the line XX--XX in FIG. 19. The device shown in FIGS. 19 and 20 is the same as the conventional semiconductor device shown in FIG. 13, except that the former has fuse portion 2 which is divided and separately arranged in two locations. Therefore, the same or corresponding portions are designated by same reference characters, and description thereof is not repeated.
FIG. 21 is a top view of a conventional semiconductor device with a fuse portion separated into two portions, illustrating its condition after laser blowing. FIG. 22 is a cross sectional view of the device taken along the line XXII--XXII in FIG. 20. In FIGS. 21 and 22, the portions same as or corresponding to the portions of the device shown in FIG. 15 are denoted by same reference characters, and description thereof is not repeated.
FIG. 23 is a diagram illustrating a problem with a semiconductor device having a fuse portion divided and arranged in two locations. FIG. 24 is a cross sectional view of the device taken along the line XXIV--XXIV in FIG. 23. The portions same as or corresponding to the portions of the device shown in FIG. 17 are designated by same reference characters, and description thereof is not repeated.
In a conventional semiconductor device, the fuse portion which has been blown by laser is most susceptible to moisture. Such a vulnerability to moisture can cause corrosion to develop at the end surface of the blown fuse portion, which will advance along the fuse portion and destroy a circuit or other fuse portions. This can make a semiconductor device defective.